Liquid esterification for the production of alcohols

ABSTRACT

Purifying and/or recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid. Separation and purification processes of crude ethanol mixture are employed to allow recovery of ethanol and remove impurities. In addition, the process involves returning acetaldehyde separated from the crude ethanol product to the reactor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional App. No.61/363,056, filed on Jul. 9, 2010, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to production of ethanol and, inparticular, to processes for esterifying a liquid stream derived fromthe crude ethanol product to improve ethanol recovery efficiencies.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, unreacted acetic acid remains in thecrude ethanol product, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

EP02060555 describes a process for esterifying ethanoic acid and analcohol to form ethanoates. The ethanoates are hydrogenated to produceethanol.

The need remains for improving the recovery of ethanol from a crudeproduct obtained by reducing alkanoic acids, such as acetic acid, and/orother carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feedstream in a first reactor to produce a crude product;removing one or more non-condensable gases from the crude product toyield a liquid stream; reacting acetic acid and ethanol in the liquidstream in a second reactor to produce an ester enriched streamcomprising ethanol and ethyl acetate; and recovering ethanol from theester enriched stream. The operating temperature of the first reactor isfrom 125° C. to 350° C. and the operating temperature of the secondreactor is lower than the first reactor and may be from 10° C. to 150°C.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol productcomprising ethanol, ethyl acetate, non-condensable gases, and aceticacid; removing one or more non-condensable gases from the crude productto yield a liquid stream; reacting acetic acid and ethanol in the liquidstream to produce an ester enriched stream comprising ethanol and ethylacetate; and recovering ethanol from the ester enriched stream.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feedstream in a first reactor to produce a crude ethanolproduct; separating a portion of crude ethanol product to produce anaqueous stream comprising water and a liquid crude ethanol productstream; reacting acetic acid and ethanol in the liquid crude ethanolproduct stream in a second reactor to produce an ester enriched stream;and recovering ethanol from the ester enriched stream.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol productcomprising ethanol, ethyl acetate, water, and acetic acid; separating aportion of crude ethanol product to produce an aqueous stream comprisingwater and a liquid crude ethanol product stream; reacting acetic acidand ethanol in the liquid crude ethanol product stream to produce anester enriched stream; and recovering ethanol from the ester enrichedstream.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a reaction system having a liquidesterification reactor in accordance with one embodiment of the presentinvention.

FIG. 2 is a schematic diagram of a reaction system that removes waterprior to esterification in accordance with one embodiment of the presentinvention.

FIG. 3 is a schematic diagram of a hydrogenation system in accordancewith one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Theethanol is recovered from a crude ethanol product comprising a mixtureof ethanol, unreacted acetic acid, and optionally ethyl acetate, andimpurities such as acetaldehyde and one or more acetals. Theconcentration of unreacted acetic acid in the mixture may vary dependingon acetic acid conversion during the hydrogenation reaction. Separatingthe unreacted acetic acid from the crude reaction mixture requiresadditional energy. To improve recovery of ethanol, in one embodiment,the present invention includes a step of esterifying unreacted aceticacid contained in the crude ethanol product, in liquid phase, to reducethe concentration of the unreacted acetic acid, and thus increase thetotal conversion of acetic acid. In this manner, since less acetic acidwill be contained the resulting crude ethanol composition, the energyrequirements for ethanol recovery may be advantageously reduced.

The hydrogenation reaction is preferably conducted in the vapor phase,and the crude ethanol product is condensed into a liquid stream (whichalso may be referred to as a crude ethanol product). In preferredembodiments, light components such as residual hydrogen are removed fromthe crude ethanol product as a vapor stream. In processes according tothe present invention, the liquid stream, optionally after removal ofthe vapor stream as discussed above, is esterified in a secondaryreactor comprising an esterification catalyst, preferably an acidcatalyst. Optionally, the liquid stream is esterified in a secondaryreactor along with a recycled portion of the recovered ethanol. Inanother embodiment, a majority of the water is removed from the liquidstream prior to esterification.

Even at relative high conversions in the hydrogenation reaction, e.g.,greater than 90 wt. %, there still may be a significant amount ofunreacted acetic acid present in the crude ethanol product. Increasingconversion, although possible, may not reduce the amount of unreactedacid to a desired level. For purposes of the present invention, the term“conversion” refers to the amount of acetic acid in the feed that isconverted to a compound other than acetic acid. Conversion is expressedas a mole percentage based on acetic acid in the feed. Selectivity isexpressed as a mole percent based on converted acetic acid. It should beunderstood that each compound converted from acetic acid has anindependent selectivity and that selectivity is independent fromconversion. Surprisingly and unexpectedly, esterifying the unreactedacid, along with a minor portion of the ethanol, allows improvedrecovery of ethanol and reduces overall energy requirements.

Liquid Esterification

FIG. 1 shows a reaction system 100 according to one embodiment of thepresent invention that comprises a hydrogenation reactor 101 and asecondary esterification reactor 102. An acetic acid feedstream 103comprising acetic acid and hydrogen is directed to hydrogenation reactor101. Reactor 101 produces a crude ethanol product 104 that is condensedand then separated in flasher 105 into a liquid stream 106 (a liquidcrude ethanol product) and a vapor stream 107. Vapor stream 107 may bereturned to reactor 101. Liquid stream 106 may comprise unreacted aceticacid depending on the acetic acid conversion. Preferably the conversionof acetic acid is greater than 60%, e.g., greater than 80%, greater than90% or greater than 95%. Of course, in order to conduct the desiredesterification reaction, some amount of unreacted acetic acid should bepresent in the crude ethanol product. In one embodiment, liquid stream106 may comprise less than 40 wt. % unreacted acetic acid, e.g., lessthan 20 wt. % or less than 10 wt. %. In terms of ranges, liquid stream106 may comprise from 1 to 40 wt. % unreacted acetic acid, e.g., from 3to 35 wt. %, or from 5 to 20 wt. %.

Liquid stream 106 is fed to esterification reactor 102. Inesterification reactor 102 unreacted acetic acid preferably reacts withethanol to form ethyl acetate, thus yielding an ester enriched stream108. Ester enriched stream 108 comprises more ethyl acetate than liquidstream 106, e.g., at least 5 wt. % more ethyl acetate, at least 10 wt. %more ethyl acetate, or at least 20 wt. % more ethyl acetate. Inaddition, ester enriched stream 108 preferably comprises less aceticacid than liquid stream 106. In one embodiment, ester enriched stream108 comprises less than 10 wt. % unreacted acetic acid, e.g., less than5 wt. % or less than 1 wt. %. In terms of ranges, ester enriched stream108 may comprise from 0.01 to 10 wt. % unreacted acetic acid, e.g., from0.05 to 5 wt. %, or from 0.05 to 1 wt. %. As a result of esterification,the total conversion of acetic acid in both reactors 101 and 102, may begreater than 90%, e.g., greater than 95% or greater than 99%.

Exemplary compositional ranges for ester enriched stream 108 in FIG. 1are provided in Table 1.

TABLE 1 ESTER ENRICHED STREAM (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Ethanol 5 to 70 10 to 60 15 to 50 Acetic Acid <10 0.05 to 5  0.05 to 1   Water 5 to 35  5 to 30 10 to 30 Ethyl Acetate <30 0.001 to20    1 to 10 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <5 0.001to 2    0.005 to 1    Acetone <5 0.0005 to 0.05  0.001 to 0.03  OtherAlcohols <8 <0.1 <0.05 Other Esters <5 <0.005 <0.001 Other Ethers <5<0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentapplication are preferably not present and if present may be present intrace amounts or in amounts greater than 0.0001 wt. %.

Embodiments of the present invention reduce unreacted acetic acidconcentration without a large penalty to overall ethanol yields.Preferably, the unreacted acetic acid concentration is reduced fromliquid stream 106 to ester enriched stream 108 by at least 40%, e.g., atleast 50%, at least 75%, or at least 85%. These reductions, however, arecoupled with a minor penalty in ethanol production. Preferably, overallethanol production is reduced by less than 10%, e.g., less than 5%, orless than 2% relative to the same system but without an esterificationunit. Although larger ethanol reductions may be possible, it isgenerally not desired to reduce unreacted acid concentrations at theexpense of significant ethanol reductions.

As shown, ester enriched stream 108 is fed to distillation zone 110 torecover an ethanol product stream 111. In some embodiments, water stream112, and/or lights stream 113 may also be separated from ester enrichedstream 108. Preferably, water stream 112 comprises any remainingunreacted acetic acid, which may be further reacted by esterification,neutralized, and/or separated from the water stream 112. The lightsstream 113, which may comprise ethyl acetate, may be recycled to reactor101. Advantageously, in some embodiments of the present invention,improved efficiencies may be realized in recovering ethanol productstream 111 from distillation zone 110, because it is unnecessary toremove residual acetic acid, or, if residual acetic acid is present,less energy is required to remove the residual acetic acid because ofits reduced concentration.

Lower conversions of acetic acid in the hydrogenation reactor are lesspreferred, e.g., less than 80%. In some embodiments, an ethanol feed 109may be fed to secondary esterification reactor 102 when there is a loweracetic acid conversion. Ethanol feed 109 is preferably taken fromethanol product stream 111. In one embodiment, up to 50% of the ethanolfrom ethanol product stream 111 is recycled as ethanol feed 109, andmore preferably up to 10%. In terms of ranges, from 1 to 50% of theethanol from ethanol product stream 111 may be recycled as ethanol feed109, and more preferably from 5 to 10%. The presence of additionalethanol in secondary esterification reactor 102 may allow an evenfurther reduction of unreacted acetic acid through esterification withethanol.

In other embodiments, optional ethanol feed 109 may be used with higherconversion of acetic acid in reactor 101, e.g., where conversion isgreater than 80%, e.g., greater than 90%, or greater than 95%.

When optional ethanol feed 109 is used, the ester enriched stream 108may also comprise more ethanol than liquid stream 106. The additionalethanol will vary depending on the amount of ethanol that is fed tosecondary esterification reactor 102 via ethanol feed 109, and esterenriched stream 108 may contain more than 70 wt. % ethanol.

FIG. 2 shows another embodiment in which a majority of the water inliquid stream 106 is removed prior to the secondary esterificationreactor 102. One or more membranes 114 are shown in FIG. 2, which removewater as the permeate 115, and the remaining portion of liquid streamforms retentate 116. The membrane may comprise a polymeric membrane, forexample, comprising polyimide hollow fibers. Alternatively, the membranemay be a zeolite membrane or a hybrid membrane with both organic andinorganic components. Suitable membranes also include shell and tubemembrane modules having one or more porous material elements therein.Non-porous material elements may also be included. The material elementsmay comprise a polymeric element such as polyvinyl alcohol, celluloseesters, and perfluoropolymers. Membranes that may be employed inembodiments of the present invention include those described in Baker,et al., “Membrane separation systems: recent developments and futuredirections,” (1991) pages 151-169, and Perry et al., “Perry's ChemicalEngineer's Handbook,” 7^(th) ed. (1997), pages 22-37 to 22-69, theentire contents and disclosures of which are hereby incorporated byreference. Retentate 116 is fed to secondary esterification reactor 102.In some embodiments, a pervaporation unit may be used in place of or inaddition to the membranes 114.

The amount of water removed prior to introduction into esterificationreactor 102 may vary, but generally membranes 114 may be capable ofremoving at least 50% of the water in liquid stream 106, e.g., at least75% or at least 85%. Although complete removal of water may be feasible,it is generally more preferred to remove from about 75% to 99% of thewater from liquid stream 106. Removing water from liquid stream 106advantageously allows the equilibrium in secondary esterificationreactor 102 to consume additional unreacted acetic acid. Using aninitial water removal step yields an ester enriched stream 108 that maycomprise less than 5 wt. % unreacted acetic acid, e.g., less than 3 wt.% or less than 0.5 wt. %. In terms of ranges, ester enriched stream 108in FIG. 2 may comprise from 0.001 to 5 wt. % unreacted acetic acid,e.g., from 0.001 to 3 wt. %, or from 0.005 to 0.5 wt. %.

Exemplary compositional ranges for ester enriched stream 108 havingreduced water according to FIG. 2 are provided in Table 2.

TABLE 2 ESTER ENRICHED STREAM (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Ethanol 5 to 85 10 to 80 15 to 75 Acetic Acid <5 0.01 to 3  0.001 to 0.5  Water <20 0.001 to 10   0.01 to 5   Ethyl Acetate <250.001 to 20    1 to 15 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal<5 0.001 to 2    0.005 to 1    Acetone <5 0.0005 to 0.05  0.001 to 0.03 Other Alcohols <8 <0.1 <0.05 Other Esters <5 <0.005 <0.001 Other Ethers<5 <0.005 <0.001

Although one membrane is shown in FIG. 2, it should be appreciated thatan array of membranes may be used in a multistep configuration to removemore water, optionally a majority of the water from liquid stream 106.Preferably, the membranes are acid-resistant membranes that selectivelypermeate water.

In FIG. 2, ester enriched stream 108 is fed to distillation zone 110 torecover an ethanol product stream 111. In some embodiments, lightsstream 113 may also be separated from ester enriched stream 108. Thelights stream 113, which may comprise ethyl acetate, may be recycled toreactor 101. Optionally, a residue stream 117 may be taken fromdistillation zone. Residue stream 117 may comprise any remaining aceticacid and/or water. In preferred embodiments, it may not be necessary toseparate residue stream 117. When separated, residue stream may compriseacetic acid that may be further reacted by esterification, neutralized,and/or separated from the residue stream. Advantageously, as discussedabove, in some embodiments of the present invention, improvedefficiencies may be realized in recovering ethanol product stream 111from distillation zone 110, because it is unnecessary to remove residualacetic acid, or, if residual acetic acid is present, less energy isrequired to remove the residual acetic acid because of its reducedconcentration.

The esterification reaction preferably is carried out in the liquidphase at a reaction temperature that ranges from 10° C. to 150° C.,e.g., from 20° C. to 100° C., or from 30° C. to 80° C. In oneembodiment, the esterification reaction is conducted at a temperaturethat is less than the hydrogenation reaction temperature. The pressurein the esterification is generally atmospheric, but may vary dependingon the hydrogenation reaction pressure and generally ranges from 10 kPato 2000 kPa, e.g., from 50 kPa to 1000 kPa, or from 100 kPa to 500 kPa.

Acid-catalyzed esterification reactions may be used with someembodiments of the present invention. The catalyst should be thermallystable at reaction temperatures. Suitable catalysts may be solid acidcatalysts comprising an ion exchange resin, zeolites, Lewis acid, metaloxides, inorganic salts and hydrates thereof, and heteropoly acid andsalts thereof Silica gel, aluminum oxide, and aluminum phosphate arealso suitable catalysts. Acid catalysts include, but are not limited to,sulfuric acid, and tosic acid. In addition, Lewis acids may also be usedas esterification catalysts, such as scandium(III) or lanthanide(III)triflates, hafnium(IV) or zirconium(IV) salts, and diarylammoniumarenesulfonates. The catalyst may also include sulfonated (sulphonicacid) ion-exchange resins (e.g., gel-type and macroporous sulfonatedstyrene-divinyl benzene IERs), sulfonated polysiloxane resins,sulfonated perfluorinated (e.g., sulfonated poly-perfluoroethylene), orsulfonated zirconia.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any acetic acidhydrogenation process for producing ethanol. The materials, catalyst,reaction conditions, and separation are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizingfollowed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The operating temperatures of thehydrogenation reactor is generally higher than the esterificationreactor. The pressure may range from 10 kPa to 3000 kPa, e.g., from 50kPa to 2300 kPa, or from 100 kPa to 1500 kPa. The reactants may be fedto the reactor at a gas hourly space velocity (GHSV) of greater than 500hr⁻¹, e.g., greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ or evengreater than 5000 hr⁻¹. In terms of ranges the GHSV may range from 50hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB, VIB,VIIB, VIII transitional metals, a lanthanide metal, an actinide metal,or a metal selected from any of Groups IIIA, IVA, VA, and VIA. Preferredmetal combinations for some exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, andruthenium/iron. Exemplary catalysts are further described in U.S. Pat.No. 7,608,744 and U.S. Pub. No. 2010/0029995, the entireties of whichare incorporated herein by reference. In another embodiment, thecatalyst comprises a Co/Mo/S catalyst of the type described in U.S. Pub.No. 2009/0069609, the entirety of which is incorporated herein byreference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.Most preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another, or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from both the first and secondmetals. In preferred embodiments, the third metal is selected from thegroup consisting of cobalt, palladium, ruthenium, copper, zinc,platinum, tin, and rhenium. More preferably, the third metal is selectedfrom cobalt, palladium, and ruthenium. When present, the total weight ofthe third metal is preferably from 0.05 to 4 wt. %, e.g., from 0.1 to 3wt. %, or from 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention, the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

The catalyst support may be modified with a support modifier. In someembodiments, the support modifier may be an acidic modifier thatincreases the acidity of the catalyst. Suitable acidic support modifiersmay be selected from the group consisting of: oxides of Group IVBmetals, oxides of Group VB metals, oxides of Group VIB metals, oxides ofGroup VIIB metals, oxides of Group VIIIB metals, aluminum oxides, andmixtures thereof. Acidic support modifiers include those selected fromthe group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, andSb₂O₃. Preferred acidic support modifiers include those selected fromthe group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, and Al₂O₃. The acidicmodifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO,Co₂O₃, and Bi₂O₃.

In another embodiments, the support modifier may be a basic modifierthat has a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. The basicsupport modifier may be selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain NorPro. The Saint-GobainNorPro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry; andpacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Süd-Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

The conversion of the hydrogenation reaction may be at least 10%, e.g.,at least 20%, at least 40%, at least 50%, at least 60%, at least 70% orat least 80%. Although catalysts that have high conversions aredesirable, such as at least 80% or at least 90%, in some embodiments, alow conversion may be acceptable at high selectivity for ethanol. Inparticular embodiments, low conversion may be used in either reactorwhen hydrogenation reactors are staged.

Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500per grams of ethanol per kilogram of catalyst per hour or from 600 to2,000 grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseunreacted acetic acid, ethanol and water. As used herein, the term“crude ethanol product” refers to any composition comprising from 5 to70 wt. % ethanol and from 5 to 40 wt. % water. Exemplary compositionalranges for the crude ethanol product are provided in Table 1. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Component Conc.(wt. %) (wt. %) (wt. %) Conc. (wt. %) Ethanol 5 to 70 15 to 70  15 to 5025 to 50 Acetic Acid 0 to 90 0 to 50 15 to 70 20 to 70 Water 5 to 40 5to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3 to 10Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to 10  0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In embodiments having lower amounts of aceticacid, the conversion of acetic acid is preferably greater than 75%,e.g., greater than 85% or greater than 90%. In addition, the selectivityto ethanol may also be preferably high, and is preferably greater than75%, e.g., greater than 85% or greater than 90%.

Ethanol Recovery

An exemplary hydrogenation system 200 is shown in FIG. 3. System 200comprises reaction zone 201 and distillation zone 202. System 200 alsocomprises an hydrogenation reactor 203 and a secondary esterificationreactor 204.

In reaction zone 201, hydrogen and acetic acid are fed to a vaporizer205 via lines 206 and 207 respectively, to create a vapor feed stream inline 208 that is directed to hydrogenation reactor 203. In oneembodiment, lines 206 and 207 may be combined and jointly fed to thevaporizer 205. The temperature of the vapor feed stream in line 208 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 205, as shown in FIG. 3, and may be recycled or discardedthereto. In addition, although FIG. 3 shows line 208 being directed tothe top of reactor 203, line 208 may be directed to the side, upperportion, or bottom of reactor 203. Further modifications and additionalcomponents to reaction zone 202 are described below.

Reactor 203 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials are known in the art andinclude, for example, carbon, silica, alumina, ceramic, or resins. Incertain embodiments of the invention, the guard bed media isfunctionalized to trap particular species such as sulfur or halogens.During the hydrogenation process, a crude ethanol product is withdrawn,preferably continuously, from reactor 203 via line 209.

Crude ethanol product 209 may be condensed and fed to flasher 210,which, in turn, provides a vapor stream and a liquid stream. The flasher210 may operate at a temperature of from 50° C. to 250° C., e.g., from30° C. to 225° C. or from 60° C. to 200° C. The pressure of flasher 210may be from 50 kPa to 2000 kPa, e.g., from 75 kPa to 1500 kPa or from100 to 1000 kPa.

The vapor stream exiting the flasher 210 may comprise hydrogen,hydrocarbons, and other non-condensable gases, which may be purgedand/or returned to reaction zone 201 via line 211. As shown in FIG. 3,the returned portion of the vapor stream passes through compressor 212and is combined with the hydrogen feed 206 and co-fed to vaporizer 205.

Optionally, crude ethanol product 209 may pass through one or moremembranes to separate hydrogen and/or other non-condensable gases.

The liquid in line 213 from flasher 210 is fed to esterification reactor204. Esterification reactor 204 contains a suitable acidic catalyst forreacting unreacted acetic acid with ethanol to yield an ester enrichedstream in line 214. Ester enriched stream 214 as indicated abovecomprises less than 10 wt. % unreacted acid and more preferably lessthan 1 wt. % unreacted acid.

Ester enriched stream in line 214 is fed to the side of first column215, also referred to as an “dilute acid separation column.” Exemplarycompositions of line 214 are provided above in Table 1. It should beunderstood that ester enriched stream in line 214 may contain othercomponents, not listed, such as additional components in the feed.

The system shown in FIG. 3 may also be used with an initial waterremoval step, as indicated above in FIG. 2. When used with initial waterremoval, ester enriched stream in line 214 may have the composition asindicated in Table 2. Further, it may not be necessary to feed esterenriched stream 214 to column 215, and ester enriched stream 214 insteadmay be fed directly to column 218.

In one embodiment, the concentration of unreacted acetic acid in line214 may be from 0.01 to 10 wt. %, e.g., from 0.05 to 5 wt. %, or from0.05 to 1 wt. %. As shown, line 214 is introduced in the lower part offirst column 215, e.g., lower half or lower third. Column 215 operatesto remove a dilute acid stream as residue 216. Dilute acid streamcomprises water and less than 30 wt. % acetic acid. In one embodiment,residue 216 may be separated into a water stream and an acetic acidstream, and either stream may be returned to reaction zone 201. In otherembodiments, the residue 216 may be treated in a weak acid recoverysystem to recover acetic acid. In still other embodiments, residue 216may be sent to a reactive distillation column to further convertresidual acetic acid to esters, preferably by reacting with methanol toform methyl acetate. In other embodiments, residue 216 may be directedto a waste water treatment facility. Generally, the organic content,e.g., unreacted acid, of the residue may be suitable to feedmicroorganisms used to treat waste water.

The present invention allows for improved recovery of ethanol using lessenergy because line 214 contains reduced amounts of acetic acid. Thus,the residue 216, as well as distillate 217, of column 215 would containminor amounts of acetic acid. In some embodiments, most of the water inline 214 may be withdrawn as the residue 216. Preferably, a majority ofthe water is withdrawn in residue via line 216 as opposed to distillatevia line 217 such that the weight ratio of water in line 216 to line 217is greater than 2:1.

First column 215 also forms an overhead distillate, which is withdrawnin line 217, and which may be condensed and refluxed, for example, at aratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

In some embodiments, when the content of acetic acid in line 214 is lessthan 5 wt. %, the column 215 may be skipped and line 214 may beintroduced directly to second column 218, also referred to herein as a“light ends column.” In addition, column 215 may be operated toinitially remove a substantial portion of water as the residue.

Any of columns 215, 218, or 221 may comprise any distillation columncapable of separation and/or purification. The columns preferablycomprise tray columns having from 1 to 150 trays, e.g., from 10 to 100trays, from 20 to 95 trays or from 30 to 75 trays. The trays may besieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. In other embodiments, a packed columnmay be used. For packed columns, structured packing or random packingmay be employed. The trays or packing may be arranged in one continuouscolumn or they may be arranged in two or more columns such that thevapor from the first section enters the second section while the liquidfrom the second section enters the first section and so on.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in FIG. 3. As shown in FIG. 3,heat may be supplied to the base of each column or to a circulatingbottom stream through a heat exchanger or reboiler. Other types ofreboilers, such as internal reboilers, may also be used in someembodiments. The heat that is provided to reboilers may be derived fromany heat generated during the process that is integrated with thereboilers or from an external source such as another heat generatingchemical process or a boiler. Although one reactor and one flasher areshown in FIG. 3, additional reactors, flashers, condensers, heatingelements, and other components may be used in embodiments of the presentinvention. As will be recognized by those skilled in the art, variouscondensers, pumps, compressors, reboilers, drums, valves, connectors,separation vessels, etc., normally employed in carrying out chemicalprocesses may also be combined and employed in the processes of thepresent invention.

The temperatures and pressures employed in any of the columns may vary.As a practical matter, pressures from 10 kPa to 3000 kPa will generallybe employed in these zones although in some embodiments subatmosphericpressures may be employed as well as superatmospheric pressures.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. It will be recognized by thoseskilled in the art that the temperature at a given location in anoperating distillation column is dependent on the composition of thematerial at that location and the pressure of column. In addition, feedrates may vary depending on the size of the production process and, ifdescribed, may be generically referred to in terms of feed weightratios.

When column 215 is operated under about 170 kPa, the temperature of theresidue exiting in line 216 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 217 from column 215 preferably is from 60° C.to 90° C., e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In otherembodiments, the pressure of first column 215 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.Distillate and residue compositions for first column 215 for oneexemplary embodiment of the present invention are provided in Table 4.In addition, for convenience, the distillate and residue of the firstcolumn may also be referred to as the “first distillate” or “firstresidue.” The distillates or residues of the other columns may also bereferred to with similar numeric modifiers (second, third, etc.) inorder to distinguish them from one another, but such modifiers shouldnot be construed as requiring any particular separation order.

TABLE 4 FIRST COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 20 to 90  30 to 85 50 to 85 Water 4 to 38  7 to 32  7to 25 Acetic Acid <1 0.001 to 1    0.01 to 0.5  Ethyl Acetate <60  5 to40  8 to 45 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <4.0 <3.0<2.0 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid <700.01 to 55   0.05 to 30   Water 30 to 100 45 to 97 60 to 95 Ethanol <1<0.9 <0.5

As indicated in Table 4, embodiments of the present invention allow amajority of the water to be withdrawn in residue line 216. In addition,this approach results in a reduction in the amount of acetic acid thatmay be carried over in the distillate line 217. Preferably, there issubstantially no or very low amounts of acetic acid in distillate line217. Reducing acetic acid in distillate 217 advantageously may reducethe amount of acetic acid in the final ethanol product and reducesoverall energy requirements in the separation steps.

Some species, such as acetals, may decompose in column 215 to low oreven undetectable amounts. In addition, to esterification reactor 204,there may also be an equilibrium reaction after the crude ethanolproduct 209 exits hydrogenation reactor 203 and prior to secondaryesterification reactor 204. Generally, the reaction may occur in line213. Depending on the concentration of acetic acid, equilibrium may bedriven towards formation of ethyl acetate. The equilibrium may beregulated using the residence time and/or temperature of liquid stream213.

The distillate, e.g., overhead stream, of column 215 optionally iscondensed and refluxed as shown in FIG. 3, preferably, at a reflux ratioof 1:5 to 10:1. The distillate in line 217 preferably comprises ethanol,ethyl acetate, and lower amounts of water.

The first distillate in line 217 is introduced to the second column 218,also referred to as a “light ends column,” preferably in the top part ofcolumn 218, e.g., top half or top third. Second column 218 may be a traycolumn or packed column. In one embodiment, second column 218 is a traycolumn having from 5 to 70 trays, e.g., from 15 to 50 trays, or from 20to 45 trays. As one example, when a 30 tray column is used in a columnwithout water extraction, line 117 is introduced at tray 2. In anotherembodiment, the second column 218 may be an extractive distillationcolumn. In such an embodiment, an extraction agent, such as water, maybe added to second column 218. If the extraction agent comprises water,it may be obtained from an external source or from an internalreturn/recycle line from one or more of the other columns. Othersuitable extractive agents that may be used include dimethylsulfoxide,glycerine, diethylene glycol, 1-naphthol, hydroquinone,N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol;propylene glycol-tetraethylene glycol-polyethylene glycol;glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethylether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine,N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamineand 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane,tetradecane, chlorinated paraffins, or combinations thereof.

In some embodiments, a portion of the water in first distillate 217 maybe removed prior to second column 218, using one or more membranes,and/or adsorptions units.

Although the temperature and pressure of second column 218 may vary,when at about 20 kPa to 70 kPa, the temperature of the second residueexiting in line 219 preferably is from 30° C. to 75° C., e.g., from 35°C. to 70° C. or from 40° C. to 65° C. The temperature of the seconddistillate exiting in line 220 from second column 218 preferably is from20° C. to 55° C., e.g., from 25° C. to 50° C. or from 30° C. to 45° C.Second column 218 may operate at a reduced pressure near or at vacuumconditions, to further favor separation of ethyl acetate and ethanol. Inother embodiments, the pressure of second column 218 may range from 0.1kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.Exemplary distillate and residue compositions for second column 218 areprovided in Table 5 below. It should be understood that the distillateand residue may also contain other components, not listed, such asadditional components in the feed.

TABLE 5 SECOND COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate 5 to 90  10 to 80 15 to 75 Acetaldehyde <60  1to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to 35   Water <20 0.01 to10   0.1 to 5   Residue Ethanol 40 to 99.5 50 to 95 60 to 90 Water <600.5 to 50  0.1 to 30  Ethyl Acetate <1 0.001 to 2    0.001 to 0.5 Acetic Acid <0.5 <0.01 0.001 to 0.01 

The weight ratio of ethanol in the second residue to ethanol in thesecond distillate preferably is at least 2:1, e.g., at least 6:1, atleast 8:1, at least 10:1 or at least 15:1. The weight ratio of ethylacetate in the second residue to ethyl acetate in the second distillatepreferably is less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1.In embodiments that use an extractive column with water as an extractionagent as the second column 108, the weight ratio of ethyl acetate in thesecond residue to ethyl acetate in the second distillate is less than0.1:1.

Returning to the second distillate, which comprises ethyl acetate and/oracetaldehyde, the second distillate preferably is refluxed as shown inFIG. 3, for example, at a reflux ratio of from 1:30 to 30:1, e.g., from1:5 to 5:1 or from 1:3 to 3:1. In some embodiments, the seconddistillate in line 220 or portion thereof may be returned reactor 203.For example, it may be advantageous to return a portion of seconddistillate 220 to reactor 203. In certain embodiments and as shown inFIG. 3, the second distillate may be fed to an acetaldehyde removalcolumn to recover aldehyde that may be recycled to the reactor 203. Thiscolumn may also separate the second distillate 220 to yield a residue,which comprises ethyl acetate. In other embodiments, the seconddistillate may be hydrolyzed or fed to an hydrogenolysis reactor (notshown) to produce ethanol from ethyl acetate. In still otherembodiments, the second distillate may be purged from system.

Optionally, when second distillate 217 comprises water, the water may beremoved using one or more membranes, and/or adsorptions units. Theremoved water may be purged or retained in the system.

The second residue 219 from the bottom of second column 218 comprisesethanol and water. Depending on the concentration of water in secondresidue 219, the water may be removed to yield an ethanol product. Insome embodiments, the amount of water in residue 219 may be sufficientfor the particular use of the ethanol product, such as for industrialuses. For uses that require lower amounts of water, in particular asfuels, the water may be removed using a distillation column, membrane,adsorption unit, or combination thereof.

As shown in FIG. 3, second residue is fed via line 219 to third column221, also referred to as a “product column.” The second residue in line219 is introduced in the lower part of third column 221, e.g., lowerhalf or lower third. Third column 109 recovers ethanol, which preferablyis substantially pure other than the azeotropic water content, as thedistillate in line 222. The distillate of third column 221 preferably isrefluxed as shown in FIG. 3, for example, at a reflux ratio of from 1:10to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to 2:1. The third residue inline 223, which preferably comprises primarily water, may be returned asan extractive agent to another column, such as the second column 218. Insome embodiments, third residue may be used to hydrolyze an ethylacetate stream, such as the second distillate 220. Third column 221 ispreferably a tray column as described above and preferably operates atatmospheric pressure. The temperature of the third distillate exiting inline 222 from third column 221 preferably is from 60° C. to 110° C.,e.g., from 70° C. to 100° C. or from 75° C. to 95° C. The temperature ofthe third residue 223 exiting from third column 221 preferably is from70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 105°C., when the column is operated at atmospheric pressure. Exemplarycomponents of the distillate and residue compositions for third column222 are provided in Table 6 below. It should be understood that thedistillate and residue may also contain other components, not listed,such as components in the feed.

TABLE 6 THIRD COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3 to 8Acetic Acid <1 0.001 to 0.1  0.005 to 0.01  Ethyl Acetate <5 0.001 to4    0.01 to 3   Residue Water  75 to 100  80 to 100  90 to 100 Ethanol<0.8 0.001 to 0.5  0.005 to 0.05  Ethyl Acetate <1 0.001 to 0.5  0.005to 0.2  Acetic Acid <2 0.001 to 0.5  0.005 to 0.2 

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns 215, 218 and/or 221 in the system200. Preferably at least one side stream is used to remove impuritiesfrom the third column 221. The impurities may be purged and/or retainedwithin the system 200.

Optionally, a portion of the third distillate 222, e.g., up to 50% ofthe third distillate, may be withdrawn via line 230 and fed toesterification reactor 204.

The ethanol product is taken from the third distillate 222. Thirddistillate 222 may be further purified to form an anhydrous ethanolproduct stream, i.e., “finished anhydrous ethanol,” using one or moreadditional separation systems, such as, for example, distillationcolumns (e.g., a finishing column), membranes, adsorption units, ormolecular sieves. Anhydrous ethanol may be suitable for fuelapplications.

The ethanol product may be an industrial grade ethanol preferablycomprising from 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % orfrom 85 to 96 wt. % ethanol, based on the total weight of the ethanolproduct. Exemplary finished ethanol compositional ranges are providedbelow in Table 7.

TABLE 7 FINISHED ETHANOL COMPOSITIONS Conc. Conc. Component (wt. %) (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol is from 80 to 1,000 wppm, e.g., from 95 to 1,000 wppm, from 100to 700 wppm, or from 150 to 500 wppm. In one embodiment, the finishedethanol composition preferably is substantially free of acetaldehyde andmay comprise less than 8 wppm of acetaldehyde, e.g., less than 5 wppm orless than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit,such as an adsorption unit, membrane and/or molecular sieve. In suchembodiments, the ethanol concentration of the ethanol product may behigher than indicated in Table 7, and preferably is greater than 97 wt.% ethanol, e.g., greater than 98 wt. % or greater than 99.5 wt. %, andless than 3 wt. % water, e.g. less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingfuels, solvents, chemical feedstocks, pharmaceutical products,cleansers, sanitizers, hydrogenation transport or consumption. In fuelapplications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used a chemical feedstockto make other chemicals such as vinegar, ethyl acrylate, ethyl acetate,ethylene, glycol ethers, ethylamines, aldehydes, and higher alcohols,especially butanol. In the production of ethyl acetate, the finishedethanol composition may be esterified with acetic acid or reacted withpolyvinyl acetate. The finished ethanol composition may be dehydrated toproduce ethylene. Any of known dehydration catalysts can be employed into dehydrate ethanol, such as those described in copending U.S. Pub.Nos. 2010/0030002 and 2010/0030001, the entire contents and disclosuresof which are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y inU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedby reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. The following examplesdescribe the various distillation processes of the present invention.

EXAMPLES Example 1

Acetic acid and hydrogen are fed to a hydrogenation reactor having acatalyst that converts about 95% of the acetic acid and has aselectivity to ethanol of about 78%. The reactor effluent comprises 5wt. % unreacted acetic acid, 52.9 wt. % ethanol, 13.2 wt. % ethylacetate, and 26.9 wt. % water. The reactor effluent is sent to a flasherto separate a liquid stream.

Example 2

The liquid stream from Example 1 is fed to an esterification reactorunder similar conditions. The catalyst for the esterification is anAmberlyst™ 15 and the esterification is conducted at a temperature of60° C. at atmospheric pressure. An ester enriched stream is withdrawnfrom esterification reactor. The ester enriched stream comprises 2.5 wt.% unreacted acetic acid, 50.8 wt. % ethanol, 16.9 wt. % ethyl acetate,and 27.8 wt. % water. The acetic acid conversion in the esterificationreactor was 50.5%, which provided a total acid conversion of 97.5%.

Example 3

The liquid stream from Example 1 along with an ethanol recycle stream isfed to an esterification reactor under similar conditions. The ethanolrecycle stream comprises 10% of the ethanol recovered by furtherseparation. An ester enriched stream is withdrawn from esterificationreactor. The ester enriched stream comprises 2.2 wt. % unreacted aceticacid, 53.3 wt. % ethanol, 16.3 wt. % ethyl acetate, and 26.4 wt. %water. The acetic acid conversion in the esterification reactor was54.3%, which provided a total acid conversion of 97.7%.

Example 4

The liquid stream from Example 1 along with an ethanol recycle stream isfed to an esterification reactor under similar conditions. The ethanolrecycle stream comprises 50% of the ethanol recovered by furtherseparation. An ester enriched stream is withdrawn from esterificationreactor. The ester enriched stream comprises 1.4 wt. % unreacted aceticacid, 60.9 wt. % ethanol, 14.1 wt. % ethyl acetate, and 22.1 wt. %water. The acetic acid conversion in the esterification reactor was64.7%, which provided a total acid conversion of 98.2%.

Example 5

The liquid stream from Example 1 is fed to one or more membranes toremove about 95% of the water under similar conditions. The liquidstream having a reduced water content is fed to an esterificationreactor. An ester enriched stream is withdrawn from esterificationreactor. The ester enriched stream comprises 0.4 wt. % unreacted aceticacid, 66.3 wt. % ethanol, 27.0 wt. % ethyl acetate, and 3.7 wt. % water.The acetic acid conversion in the esterification reactor was 94.0%,which provided a total acid conversion of 99.7%.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol comprising: hydrogenatingacetic acid from an acetic acid feedstream in a first reactor to producea crude product; removing one or more non-condensable gases from thecrude product to yield a liquid stream; reacting the acetic acid andethanol of the liquid stream in a second reactor, under esterificationconditions, to produce an ester enriched stream comprising ethanol andethyl acetate; and recovering ethanol from the ester enriched stream,wherein the ester enriched stream comprises less than 10 wt. % aceticacid.
 2. The process of claim 1, wherein at least a portion of therecovered ethanol is added to the second reactor.
 3. The process ofclaim 1, wherein the liquid stream comprises less than 40 wt. % aceticacid.
 4. The process of claim 1, wherein the ester enriched streamcomprises 0.01 wt. % to 10 wt. % acetic acid.
 5. The process of claim 1,further comprising providing an alcohol stream to the second reactor. 6.The process of claim 5, wherein the alcohol stream comprises less than50 wt. % of the recovered ethanol.
 7. The process of claim 1, whereinthe conversion of acetic acid in the second reactor is greater than 40%.8. The process of claim 1, wherein the total conversion of acetic acidin the first and second reactor is greater than 90%.
 9. The process ofclaim 1, wherein the first reactor comprises a different catalyst thanthe second reactor.
 10. The process of claim 1, wherein the firstreactor comprises a hydrogenation catalyst selected from the groupconsisting of platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron.
 11. The processof claim 1, wherein the acetic acid is formed from methanol and carbonmonoxide, wherein each of the methanol, the carbon monoxide, andhydrogen for the hydrogenating step is derived from syngas, and whereinthe syngas is derived from a carbon source selected from the groupconsisting of natural gas, oil, petroleum, coal, biomass, andcombinations thereof.
 12. The process of claim 1, wherein the secondreactor comprises an acid catalyst.
 13. The process of claim 1, whereinthe first reactor operates a temperature from 125° C. to 350° C. and thesecond reactor operates a temperature from 10° C. to 150° C., whereinthe operating temperature of the second reactor is lower than theoperating temperature of the first reactor.
 14. A process for producingethanol comprising: providing a crude ethanol product comprisingethanol, ethyl acetate, non-condensable gases, and acetic acid; removingone or more non-condensable gases from the crude product to yield aliquid stream; reacting the acetic acid and ethanol of the liquid streamin a reactor, under esterification conditions, to produce an esterenriched stream comprising ethanol and ethyl acetate; and recoveringethanol from the ester enriched stream, wherein the ester enrichedstream comprises less than 10 wt. % acetic acid.
 15. A process forproducing ethanol comprising: hydrogenating acetic acid from an aceticacid feedstream in a first reactor to produce a crude ethanol product;separating a portion of crude ethanol product to produce an aqueousstream comprising water and a liquid crude ethanol product stream;directing in the liquid crude ethanol product stream to a second reactorto react the acetic acid and the ethanol to produce an ester enrichedstream; and recovering ethanol from the ester enriched stream, whereinthe ester enriched stream comprises less than 10 wt. % acetic acid. 16.The process of claim 15, wherein the aqueous stream comprises at least75% of the water from the crude product.
 17. The process of claim 15,wherein the step of separating a portion of crude product is conductedby passing the portion of crude product through a membrane to yield apermeate comprising the aqueous stream and a retentate comprising theliquid crude ethanol product stream.
 18. The process of claim 15,wherein the step of separating a portion of crude product is conductedby feeding the portion of crude product to a pervaporation unit.
 19. Theprocess of claim 15, wherein at least a portion of the recovered ethanolis added to the second reactor.
 20. The process of claim 15, wherein theliquid crude ethanol product stream comprises less than 40 wt. % aceticacid.
 21. The process of claim 15, wherein the ester enriched streamcomprises from 0.01 wt. % to 10 wt. % acetic acid.
 22. A process forproducing ethanol comprising: providing a crude ethanol productcomprising ethanol, ethyl acetate, water, and acetic acid; separating aportion of crude ethanol product to produce an aqueous stream comprisingwater and a liquid crude ethanol product stream; reacting the aceticacid and ethanol of the liquid crude ethanol product stream in areactor, under esterification conditions, to produce an ester enrichedstream; and recovering ethanol from the ester enriched stream.